1. Field of the Invention
The present invention relates to solar heaters, and particularly to solar heaters of the type utilizing a vaporizable refrigerant to effect heat transfer to a heat storage means.
2. Description of the Prior Art
Conventional solar heating systems can be broadly categorized as either passive or active. A passive system is effective to collect heat during the day to heat the building interior, but during the night an unacceptable heat loss occurs unless the collector air space is manually or automatically covered with insulation during the night. This introduces an undesired system complexity. In addition, the enclosed air spaces in a typical passive system become uncomfortably hot during the day in order to store enough heat for significant heating at night.
Active heating systems require circulation of fluids such as air, water, ethylene glycol and the like, through the collector portion of the system during the day. This makes the system complex and expensive since recirculation pumps or fans are required. In addition, associated controls are required to halt such fluid circulation at night. The added components and moving parts in such a system typically result in a much shorter service life compared to passive heating systems.
An interesting variation on the foregoing systems is an apparatus disclosed in U.S. Pat. No. 4,073,284, issued Feb. 14, 1978, and entitled "Process and Device for Utilizing Meteorlogical Radiations". This system uses a heat storage material to store energy in the form of latent heat rather than sensible heat, thereby tending to avoid some of the problems of passive systems. A heat storage material is used whose temperature of crystallization coincides with the desired process temperature. Heat is stored in the material by changing its phase from solid to liquid at a predetermined process temperature. However, the system utilizes wicking to effect movement of refrigerant in opposition to the force of gravity, and this results in a relatively complex structure. An important consideration in a suitable solar heater is simplicity of construction to reduce initial cost and prolong service life.